for…of循环完成后，变量的值是多少？

Question

I have an application for using the final value of an array as the default. I tried:

x = [1, 2, 3];
for (var zz of x) {};
console.log(zz);   // 3

This is exactly what I wanted, but I was wondering if this is defined behavior of a for...of loop or just a fortuitous result of the implementation. I couldn't find the answer, so was hoping someone here could answer that (preferably with a reference).

Clarification: The answers and comments thus far are a bit off point. The example above shows that the final value is, in fact the last value of the array. My question is that just an unspecified result of the implementation of the formal definition of the for..of loop, or part of the formal definition.

Answer 1

zz is declared using var , so it is "hoisted" . This means that the scope extends outside of the for loop.

Since 3 was assigned to zz at the end, zz will be 3 when the loop finishes.

Answer 2

I think what I was looking for was in the ECMA spec . The use case is in 13.7.5.11:

IterationStatement : for ( var ForBinding of AssignmentExpression ) Statement
    1. Let keyResult be the result of performing ? ForIn/OfHeadEvaluation(« »,  AssignmentExpression, iterate).
    2. Return ? ForIn/OfBodyEvaluation(ForBinding, Statement, keyResult, iterate, varBinding, labelSet).

When you slog through 13.7.5.12-13, with those parameters, it appears boil down to everyone's observation (though maybe not quite as obvious as a = 5:-). So check to jh314 for saying that first.